The heart and body produce hundreds of specific sounds, including heart, lung, bowel, circulatory and Korotkoff sounds. These sounds and combinations thereof are indicative of normal and abnormal conditions. Knowledge of these sounds provides valuable diagnostic information to the physician. The art of listening to these sounds and using them as diagnostic aids is known as auscultation. Early human beings have been able to listen to these sounds by placing the ear to the chest or back of the patient. Later, the air column stethoscope was developed. The stethoscope has proven to be a valuable instrument for medical professionals. The standard air column stethoscope used by the medical profession employs a listening cup placed on the chest or back of the patient with the sound amplified by a simple bell and diaphragm into a standing air column terminating in earpieces for the physician's ears.
The conventional stethoscope has remained relatively unchanged since the last century. Many problems exist with the use of conventional stethoscopes. In general, conventional stethoscopes offer very subjective information. For example, the hearing capability of the user has direct impact on the sounds observed. When a loud sound is followed by a soft sound, difficulty exists in detecting and assessing the intensity of the soft sound. It is difficult to time an abnormal heart sound with respect to the phase of the heartbeat, an important aspect of murmur diagnosis. A fast beating heart can make both the recognition and timing of abnormal sounds difficult. This problem is often found with children and animals where heart rates are often much higher than in adult humans. External noise may often mask heart, lung, circulatory and Korotkoff sounds detected under non-ideal listening conditions. These and many other problems plague the conventional stethoscope.
In response, the field has developed electronic stethoscopes that detect and display as waveforms both audio (heart sound) and ECG (heart electrical activity), as well as presenting the heart sounds aurally. Little et al. (U.S. Pat. No. 4,362,164) describe a stethoscope having a detector head that includes a microphone and is selectably connectable to either a conventional chest-bell or an electrode chest-bell. The electrode chest-bell is adapted to pick-up electric heart signals, and the microphone to pick up body sounds. The electrode and microphone signals are sent to a separate monitoring unit to display both ECG and phonocardiographic waveforms. The conventionally detected body sounds are transmitted via air column tube directly to the user's ears. However, the Little device, and others like it, require connectivity (either via interconnect cable of wireless transmission) between the stethoscope and a separate display unit, and they are not easily transported about a physician's or other care staffs person. Again, although these devices also may be useful for their intended purpose, they too have their limitations.
Most efforts at visual display of heart data have been directed to the electrocardiographic wave pattern. Because the electrocardiographic wave pattern, i.e., the electrical wave pattern generated by the heart, is more easily processed and displayed, the electronic monitoring, displaying and storing of the electrocardiographic wave pattern has been addressed. Many patents deal with the detection, storage and display of the electrocardiographic wave pattern. Early efforts to visually display heart data were disclosed by Vogelman in U.S. Pat. No. 3,921,624. Shimoni in U.S. Pat. No. 4,617,938 and Citron in U.S. Pat. No. 4,417,306 disclosed systems for acquiring and recording electrocardiographic wave patterns. Further, Lisiecki disclosed a transfer of the recorded signals to a fixed computer for visual display. Anderson in U.S. Pat. No. 4,628,327 disclosed the acquisition, digitalization and storage of electrocardiographic wave patterns in a circular memory. Upon tripping of an alarm indicating a preset abnormal condition, the attached recorder rapidly produces a visual output of the stored data both before and after the event which tripped the alarm. Yoneda in U.S. Pat. No. 4,779,199 similarly disclosed acquisition and digitalization of the electrocardiographic wave pattern. Further, U.S. Pat. No. 4,115,864 and U.S. Pat. No. R 29,921 both disclosed the acquisition and storage of electrocardiographic wave pattern data followed by a display of that data with previously recorded electro cardiographic wave patterns to permit a visual comparison of the results by the physician.
As the above patents illustrate, most efforts at electronic storage and display of heart data have been directed to the electrocardiographic wave pattern. This is because the ECG wave pattern is much simpler and at a significantly lower frequency than the phonocardiographic heart sounds. Detection, digitization, storage and display of the phonocardiographic heart sounds are complicated by the presence of many other body sounds and by their higher frequency and more variable wave pattern. However, some work has been done in this area. Slavin in U.S. Pat. No. 4,483,346 disclosed a portable device for recording both an electrocardiographic wave pattern and phonocardiographic sounds. The phonocardiographic sounds were digitalized and stored for later transmission through a modem to a computer for storage and display. In U.S. Pat. No. 4,624,263, Slavin added cassette storage capability to the previously disclosed portable recorder. Further, Slavin disclosed the storage of abnormal phonocardiographic information for displaying with the patient's heart sounds to illustrate differences.
Although these devices may be useful for their intended purposes and may overcome some of the limitations of the classic air column stethoscope's dependence on the inherent energy contained in the original body sound, they do not address the issue that aural auscultation alone may not be sufficient to perform an adequate diagnosis, particularly of heart condition and are integrated into the chest piece or converting the conventional stethoscope into an electronic stethoscope.
Heart Failure—Congestive heart failure (CHF) is defined as impairment of systolic and/or diastolic function of the heart, leading to failure to meet the demands of peripheral tissues, or leading to maintenance of cardiac function under higher filling pressures.
In other words, CHF is a complex clinical entity that is characterized by ventricular dysfunction and compensatory neuron-hormonal alteration accompanied by exercise intolerance, fluid retention, and decreased life expectancy.
In CHF, the renin-angiotensin-aldosterone system and the sympathetic nervous system are considered to be of the utmost importance. These 2 interrelated systems regulate vascular tonus, heart rate, and contractility. CHF may stem from diastolic or systolic dysfunction.
In general, the 5-y mortality rate has been around 75% for men and 65% for women with CHF, whereas the 1-y mortality rate for severe and moderate forms of the disease reaches 40% to 50% and 15% to 25%, respectively. Coexistence of systolic and diastolic dysfunction is a frequent finding in CHF. Systolic dysfunction, in particular, is considered to be much more important in predicting the morbidity and mortality rates of the disease.
Echocardiographic evaluation of left ventricular ejection fraction (LVEF) obtained via the Simpson method has been an important parameter in the evaluation of systolic function, whereas atria-ventricular diastolic inflow waves have been obtained to assess diastolic function of the heart. Myocardial performance index (MPI) (Tei index) has been regarded as an important parameter in the evaluation of ventricular systolic function in congestive heart failure. MPI is defined as the sum of isovolumic relaxation time (IVRT) and isovolumic contraction time (IVCT) divided by left ventricular ejection time (LVET) ([IVRT+IVCT]/LVET). MPI is a Doppler-derived time interval index that combines both systolic and diastolic cardiac performance. The Tei index has been difficult to derive by using conventional non-Doppler pulsed echocardiography.
Therefore, it would be beneficial to have a versatile accessory to the conventional stethoscope that is easily portable, and has the capability to monitor and display at least heart sounds and heart electrical activity, as well as preserving the usual auscultation purposes of the conventional stethoscope that aids clinicians in diagnosing comprehensive heart issues.